Such internal combustion engines are understood in general and are operated by supplying an air-fuel mixture to the combustion chamber during the intake stroke. To create the air-fuel mixture, fuel injectors inject and atomize a predetermined fuel quantity into an intake pipe, which is connected to the combustion chamber via an inlet opening. A throttle valve situated in the intake pipe determines the quantity of fresh air to be aspirated in the direction of the combustion chamber. Opening of the throttle valve causes an increase in pressure in the intake pipe, thereby reducing the evaporation tendency of the injected fuel. Together with fuel sprayed by the injector onto the intake pipe wall, fuel is also deposited on the intake pipe wall because of the reduced evaporation tendency when the throttle valve is opened. In the case of closing of the throttle valve, the pressure in the intake pipe declines, the evaporation tendency increases and fuel deposited on the wall evaporates into the intake pipe, whereby the air-fuel mixture is enriched. In both cases, the fuel quantity supplied to the combustion chamber or the actual fuel quantity differs from the fuel quantity provided or the setpoint fuel quantity.
It is therefore believed to be understood in general that the fuel quantity provided, which is injected into the intake pipe, is to be adjusted, so that losses or additional fuel quantities, resulting from the deposition of fuel on the wall, for example, are compensated for in the event of a load change.
This procedure is referred to as transition compensation and is discussed in DE 10 2007 005 381 A1, for example. Within the scope of an economically and ecologically meaningful transition compensation, it is necessary, on the one hand, to know how great the change in fuel quantity required for the compensation for the particular operating situation should be and, on the other hand, to utilize this knowledge to correct the predetermined fuel quantity independently of operating parameters, such as the intake pipe pressure, for example. The more accurate the knowledge of the necessary change in the fuel quantity for the transition compensation, the more accurate will be the adaptation of the transition compensation. If there is no transition compensation or if it is wrong, there is the risk that the air-fuel mixture in the combustion chamber will become too rich or too lean. Under these circumstances, there may then be a power dip or even misfiring may occur. On the other hand, the accurate determination of the fuel quantity required for the transition compensation allows low-emission and uniform operation of the internal combustion engine.
To determine the compensation quantity, the property of the wall film in the intake pipe may be used. The fuel quantity deposited and thus the property of the wall film, in particular its thickness, depend on numerous parameters such as the intake pipe temperature, the intake pipe pressure and the rotational speed, for example. It is therefore advantageous to know the property of the wall film as a function of these parameters, in particular for various operating situations, and to be able to adapt the transition compensation under various conditions with knowledge of this dependence. It is customary here to control the injected fuel quantity with the aid of a control device or with the aid of a control unit as a function of the operating situation and thereby take into account the corresponding required transition compensation, in particular in the event of sudden load variations.
If the individual dependence of the change in the fuel to be injected required for the transition compensation as a function of various parameters is known, in particular the intake pipe pressure for each internal combustion engine, and if the transition compensation has been adapted for each operating situation, the possibility cannot be ruled out that the change in the fuel quantity required for the transition compensation will itself change over time. In fact it should instead be assumed that the property of the wall film and thus also the change in fuel quantity required for the transition compensation, for example, will change over time due to impurities in the intake pipe or the like. Compensation of such variations requires that the transition compensations must be adapted again in order to ensure what may be a low-emission operation of the internal combustion engine. Repeated adaptation of the transition compensation using methods from the related art is thus both expensive and time-consuming and is associated with great complexity.